The present invention relates to improvements in extended interaction oscillators (EIO) and Extended Interaction Klystron amplifiers (EIK), and especially to the mechanical tuning arrangement of the EIO or EIK resonant cavity such as to provide a large tunable frequency range.
The Extended Interaction Oscillator and Extended Interaction Klystron are vacuum tubes originally designed to convert direct current to R.F. power. Such devices are disclosed for instance in "Introduction to Millimeter Extended Interaction Klystrons", Varian Canada Technical Publication, April 1982. Both devices include a single resonator cavity containing a length of delay line, the cavity being arranged such that an electron beam is caused to pass therethrough.
In an EIO the gap length is sized such as to interact with the electron beam so as to induce monotron oscillation in the cavity. In an EIK the gap length is reduced and/or the R.F. loading increased such as to give a non-oscillating resonance to the cavity, so that a plurality of cavities may be arranged along and interacting with the electron beam to form an amplifier.
Mechanical tuning of the oscillation frequency in the prior art devices is provided by an inductive tuner in the wall of the resonant cavity such that it usually resonates at, but is not limited to, the Pi-frequency of the delay line, i.e. when adjacent gaps of the delay line are electronically 180.degree. out of phase.
A disadvantage of this method of tuning is that the tuning range of the oscillation frequency is limited because the interaction frequency of the delay line is fixed and is not a function of the tuner position. The tuning range is usually limited to about 4%. As the main resonant mode of the cavity is tuned, higher order resonant modes are also tuned. However, during tuning, the natural Pi-frequency of the delay line remains constant. On progressively tuning the resonator, the Pi-mode frequency of the delay line is "pulled" by the main cavity mode until the tuned frequency of a higher order cavity mode approaches the natural Pi-frequency of the delay line, whereupon the oscillation returns to that frequency, taking on the form of the higher order mode.
Another disadvantage of the prior art tuning method is that it is technologically difficult, if not impossible, to realize both mechanically and electrically at sub-millimeter frequencies where the cavity and structure sizes are as low as about a few microns.